Direct fired bell annealer



March 6, 1962 J. HUEBLER ETAL DIRECT FIRED BELL ANNEALER 3 Sheets-Sheet 1 Filed June 18, 1956 lnventors Jac( Huelo'le'` Carroll Cone William H. Da|ey,J^.

John D. Nesbitt,

March 6, 1962 1. HUEBLER ETAL DIRECT FIRED BEJLL ANNEALER 3 Sheets-Sheet 2 Filed June 18, 1956 lrventors JacK 'Hueloler Carroll Cone William H. Da|ey,Jr.

John D. Nesbi'bt 35/ 7// OF ,EL-'6555 Unite States &seems Patented Mar. 6, 1962 ice Ohio

Filed June 18, 1956, Ser. No. 592,l65 Claims. (CI. 263-40) This invention relates generally to heat treating apparatus and more particularly to an improved single stand bell type furnace for annealing a charge of coiled sheet metal.

Single stand annealing cover furnaces have come into favor with the present trend in the sheet metal field for deep drawing metals involving higher annealing temperatures and generally smaller unit orders for such metals. These furnaces essentially consist of a base upon which the coils are stacked, a removable inner cover on said `base forming therewith a heating chamber, a fan in the base for circulating atmosphere in the heating chamber and 'a refractory lined heating cover disposed over the inner cover and adapted to supply heat to the inner cover.

In such an annealin-g furnace there has been a nonuniform heating of the stack of coil metal, the top coil usually being overheated; and a prolonged period has been required to bring the lower coils of 'a stack to the desired temperature.

There are several factors which combine to eect the non-uniform heating, among which are the following: the relatively large cold mass of the base and the work support; non-uniform "wind" or atmosphere distribution within the inner cover; and the natural tendency for the hot products of combuston to rise to the top of the combuston chamber or space defined by the inner and outer covers.

In heating or cooling a charge of coiled metallic strip in annealing cover furnaces, it should be appreciated that there are two distinct heat transfer processes. Outside of the inner cover but 'within the outer cover radiative heat transfer occurs between the walls where the combuston takes place and the inner cover, while convective heat transfer occurs between the flame and the lue gases and hence to the inner cover. Within the inner cover, radiative heat transfer occurs primarily between the inner surface of the protective inner cover and the outer wraps of the coils while convective heat transfers 'between the inner cover and the circulating atmosphere and hence to the inner and outer coil wraps and the coil ends.

In single stand 'annealers heretofore employed, heated by banks of horizontal radiant tubes or 'banks of targen` tially fired burners, a change in heat distribution from top to bottom could only be obtained by reducng the fuel input. Vertical tubes or direct firing systems depending on updraft alone provide little or no control of vertical distribution except that Originally designed into the system by way of burnelayout. With such types of annealers, maintaining a maximum firing rate usually results in overheating the top coils. To prevent such overheatng, operators have to cut down heat input which results in decreased annealing production.

The present invention provides a bell type anne'aler with a tubeless combuston system wherein the distribution of temperature from the top to the bottom is controlled without afiecting the firing rate, and wherein the top coils are not overheated at maximum firing rate.

The increased application of forced circulation to equipment used for heating and cooling has added to the importance of convection as a process of heat transfer. Since convective heat transfer within the inner cover depends upon "wiping" heat off the protective inner cover and deliven'ng it to the coils, apparatus for directing the circulating atmosphere in paths contiguous to the side walls of the inner cover is desirable to efiect maximum heat transfer to said atmosphere from the inner cover.

Bafiies within the inner cover` have been suggested to direct the atmosphere in such contiguous paths. However, these Walls extend substantially the entire height of the inner cover and are objectionable in that effective radiative heat transfer is decreased.

It is accordingly an object of the present invention to provide improved apparatus for directing the circulating atmosphere in a furnace in paths contiguous to the side walls of the inner cover which does not substantially decrease heat transfer by radiation from the side walls of the inner cover.

In carrying out the invention, we provide a circumferential recess in the outer cover to form a firing track which tends to isolate the burning gases from the surrounding flue gas 'and 'because of the increase in wall area, to transfer heat by convection from the burning gases (to the three walls) with no increase in area to lose heat by radiation, the track will run much hotter and elminate the combuston stability problem. The com-v bustion heat is released at the bottom of the combuston space so as to transfer the major portion of that heat opposite the bottom coil of the stack and thus compensate for the tendency of the top coil to reach temperature first.

it is to be understood that the term outer cover" includes the upstanding peripheral Wall extending from the base super structure as distinguished from the term hood which refers only to the portable portion of the outer cover.

Fuel and air are tangentially fired into the track where they are retained by centrifugal force until mixing is complete and combuston occurs. When all of the air is supplied into the firing track, combuston is completed there, thus combining high temperature and high heat release to the bottom of the furnace. When part of the air is supplied at lower velocity through secondary ports near the firing track, combuston occurs in a series of spirals advancng toward the top of the combuston chamber.

By regulating the proportionate amounts of air introduced through the tangenital ports and that through the radial ports it is possible to control the completion of combuston and concomitant high heat release at the desired elevation in the combuston chamber.

The total heat input to the annealer remains unchanged and its distribution can be regulated to maintain even temperature in top and bottom coils Without nay change in the basic firing rate. Thus the invention provides controlled distribution at high heat input heretofore not provided in annealing covers with the only limitation on heat input being the ability of the wo-rk to absorb the heat.

The apparatus of the invention also provides for a nozzle for directing the circulating atmosphere longitudinally of the inner cover. The nozzle is defined by a flange in a portion of the inner cover side Wall. The fiange is preferably Secured to and made an integral part of the inner cover so as to maintain a concentrc peripheral nozzle passage whenever the inner cover is placed over the base of the furnace.

The nozzle construction of the invention provides a means of directing the circulating atmosphere contguous to the inne-r cover sidewall without substantially decreasing the effective heat transfer by radation in a manner which also results in a substantial savings of expensive alloy steel usually employed in inner cover construction. Such nozzle construction also serves as a means for directing the coldest wind past the area of greatest heat release. For a consideration of what we believe to be novel and our invention, attention is directed to the following description taken in connection With the accompanying drawings in which like characters are to designate the same or similar parts throughout the several figures of the drawing:

FIGURE 1 is a side elevational view of a single stand bell annealer with the hot track" incorporated in the base of the annealer, shown in connection with a schenatic representatior of Controls there'for;

FIGURE 2 is a sectional plan view taken along line 2-2 of FIGURE 1;

FIGURE 3 is a side elevational View of another single stand annealer with the hot track incorporated in the outer annealing hood;

FIGURE 4a is an enlarged fragmentary cross-section of the firing track or recess, together with a pilot recess;

FIGURE 4b is a cross-section of a track formed by a recess in the bottom end of the outer hood;

FIGURE 4c is a cross-section of a firing track formed by providing the refractory of the outer cover with a lip or ledge;

FIGURES 4d, 4e, and 4 are cross-sections of alternate forms of firing tracks;

FIGURE 5 is a graph showing the relationship of track temperature to depth of recess or firing track, and concomitant flue gas temperatures;

FIGURE 6 is an enlarged sectional View of the nozzle construction of PIG. 1;

FIGURE 7 is a fragmentary plan view showing the mode of annexing the nozzle fiange to the inner cover as shown in FIGS. 1 and 6; and

FIGURE 8 is a view similar to FIGURE 7 showing an alternate mode of annexing the nozzle flange to the inner cover.

The furnace illustrated in FIGURE l comprises a portable heating hood 10 for heating a bell-type muie or inner cover 11 disposed over a cylindrical column 12 of coils of sheet metal which is to be annealed. The base of the furnace is generally indicated at 15 and comprises a peripheral wall 16 on which the heating hood 10 is seatecl, the seat being surrounded by a conventional sand seal 17. The furnace base 15 also comprises a stand 18 for supporting the column of coils 12. The stand 18 is provided with a top plate 19 having a central aperture 20 co-axial with a circulating fan 23 which is driven by a motor 24. The inner cover 11 is supported on bottom plate 2.6 of ledge 27 which surrounds the coil stand 18. The top plate 19 iS separated from the bottom plate 26 by radial spacers 28 which define radial gas passages between said plates 19 and 26 for the atmosphere circulated by the fan 23. A defiector 29 may be incorporated in the stand 18 to assist in initially directing the atmosphere longitudinally of the inner cover 11.

In the single stand annealers used to anneal steel, separators are usually employed between the several coils in the column 12, to separate the coils and provide atmosphere. circulation circuits therebetween.

The foot 38 of the inner cover is surrounded by a layer of granular scaling material 31 to prevent objectionable leakage of gas from the inner cover, it being understood that some seepage of gas is not objectionable but rather desirable. A non-oxidizing atmosphere gas is supplied to the inner cover 11 by a supply pipe not shown but which extends through the coil stand 18 from below.

For heating the furnace in accordance with the invention, a plurality of gas burners 34 are provided within a circumferential recess forming a hot track" 35 in the peripheral wall 16 as shown in FIG. 1. Such a hot track" may be placed in the bottom portion of hood 10 as shown in FIG. 3. Whether the burners 34 and hot track? are constructed as part of the base 15 or part, of the hood 10 is a matter of economics of an individual installation. In those installations where one hood 10 is used in. operation With several bases it may be more economical to place the hot track in the hood; however,

such Construction has the disadvantage of requiring the disconnection and connection of the fuel and air supply lines each time the hood is moved to another base.

An annular supply passage 37 furnishes tangential highvelocity air to the ports 38 for combustion with the gas.. Tangential firing into the track 35 provides a fast spirr to the fuel and air which produces rapid efiicient mixing: and retention of heat near the bottom of the combustion chamber 40 defined as the annular space between the hood 19 and the inner cover 11. The track 35 becomes hot very quickly :and thus provides a means of maintainingi stable igniton.

The cross-section of the track 35 may be one of several as shown in FIGS. 4a, 4d, 4e and 4 or it may also be forrned by providing a lip or ledge on the sidewall 13 of the hood as indicated in FIGS. 4b and 40.

It is preferable that the depth (d) of the track or recess 35 be at least /2 of its height (h). Such relationship not only insures stable igniton or combustion in a cold outer cover, but also provides intense heat radiation. As the track is deepened, the track temperature and the radiation intensity will increase.

Conveetion heat from the fiame of the corn busted mix- -ture beats the walls of the track. The heat from the track is in turn radiated to the inner cover, and in a steady state of heat flow this transfer may be expressed by the formula In practice h is generally found to be of the order of 10` while h is found to have an average value of 15 when T is assumed to be a cold body of approximately F. If T is assumed to be 2500" F., which is a good practical average, then From the above formula, which is based upon the above reasonab le assumptions, the following table may be calculated for the track temperatures produced in tracks having various depth to height relationships.

i d Ta F. i'd-HE 1 0 1, 000 %h l, 470 l h 1, 700 0 a 2, 500

It may be observed that to attain a temperature of 1400 F., deemed in` the industry to be necessary to maintain safe ignition conditions, the track depth should be approximately /2 the track height. Obviously any greater' depth to height ratio would result in a higher temperature. is also to be noted that merely firing into a chamber without a hot track" (the condition indicated where d=0) will not produce safe ignition temperatures.

Structural limitations in individual furnace designswilldictate the depth of track. In those installations where structural limitations of a track prohibit having a suflicient depth to maintain ignition when firing at a cold body, a smaller annular pilot recess 41 in cooperation with the track may be employed to maintain continuous ignition of the fuel mixture upon entry into the track. Such an ignition pilot recess is shown in FIG. 4a. The fiame which is to be burned in such pilot recess 41 is introduced into the recess by a pluralty of circumferentially spaced pilot burners (not shown) much in the same manner as the main burners 34 fire the hot track."

For a given firing rate, the larger the ratio of track depth to track height, the higher will be the track temperature and the more intense will be the heat transfer by radia-tion to the inner cover area looking at the track. As the localized radiation becomes more intense, the flue gases leaving the track become cooler. This relationship is graphically shown by the curves of FIG. 5. Since the flue gases leave the track at reduced temperatures, they have less available heat to be transferred to the inner cover as they ascend the heating chamber. This phenomenon means that as the depth of the track is increased, the percentage of heat transfer occurring at the bottom of the combustion chamber 40 to the area looking at the hot track" is increased.

When it is desirable to retain most of the heat near the bottom of the combustion chamber 40 all of fuel and air is introduced through the tangential ports 38 in the track 35 where they are retained by centrifugal force until miXing is complete and combustion occurs.

An annular passage 42 provides low velocity air to a plurality of radial or secondary ports 43. These ports 43 are located a few inches below the hot track 35 and preferably in vertical alignment with the tangential ports. When a portion of the combustion air is introduced to the tangential ports and the remaining air required to complete combustion is introduced to the radial ports combustion occurs in a series of spirals which ascend the combustion chamber 40. By varying the ratio of the track and radial port air it is possible to regulate the elevation where combustion is completed and high heat release occurs.

The temperatures of the bottom and top coils in the inner cover 11 are measured by thermocouples 45 and 46 respectively. The thermocouples are electrically connected through their respective leads 450 and 46a to the recording temperature control 47 which in turn through suitable relays actuates the servomotor 48 which regulates the opening and closing of Valve 49 in the air supply line 59 thereby proportioning the air to passages 37 and 42 and subsequently through the tangential and radial air ports.

lt is to be understood that all of the air may be introduced to the hot track while the fuel is proportioned between primary tangential ports in the hot track and secondary radial ports either below or above the primary fuel ports as a means to vary the heat release to the various areas of the combustion chamber.

The furnace temperature is maintained by re-gultaing the total fuel and air input which is controlled by valves 51 and 52 respectively which in turn are operatcd by servomotor 53. The servomotor 53 is energized by the temperature sensing device 54 connected by lead 5551 to a third thermocouple 55 mounted in the stand 18.

For optimum results, the concentration of heat to the outside area of the inner cover looking at the hot track" should be matched by heat transfer within the cover. The invention provides a novel nozzle construction for directing the coldest atmosphere or wind within the inner cover past this area of greatest heat release.

In the single-stand annealers heretofore employed, the coldest atmosphere or wind in the circuits is that leaving the bottom col and entering the fan. As this wind rises between the inner cover and bottom col it is heated by contact With the inner cover. Since all of the recrculating wind from the fan passes this point the wind cools 6 the inner cover in this area the maximum amount, but is heated a minimum number of degrees. This phenomenon causes the wind in the circuit between the bottom two coils of a stack to be the coolest. Thus the convection heat transfer from the wind to the bottom coil is at a minimum. Since the inner cover area adjacent the bottom col is cooled, the radiation heat transfer in this area s also at a minimum. Laboratory experiments indicate that convection currents actually remove heat from the bottom coil in furnaces, heretofore employed during a portion of the charge heating cycle.

The portion of the wind rising between the inner cover and the second col is less in mass because some of the wind has been diverted to the Separator interposed between the bottom and second coils and hence is warmer. The cooling etfect on the inner cover in this area is reduced because the wind is warmer and the mass flow is decreased. Thus the wind leaving this area and entering the second Separator is heated a greater number of degrees resulting in a greater heating efiect on the second coil than on the bottom coil.

This phenomenon becomes more pronounced as the remaining atmosphere rises to the progressively higher coils and results in heating the outside top corner of the topmost coil to its maximum permissible temperature in a relatively short time. This quick heating of the top coil forces the combustion rate to be curtailed early in the charge heating cycle thus requiring many more hours of heating in order to bring the bottom coil to the minimum permssible temperature and also results in a heating cycle approxirnately twice that required when all of the coils are heated at the same rate. This represents a serious loss in annealing production of an individual annealer.

Experience has shown that moderate concentration of heat at the bottom as obtained by directing the flame of the burners toward the bottom of the inner cover does not give uniform heat input to the charge but results in overheating the top of the range.

ldeally, the atmosphere within the inner cover should be heated instantaneously to the final desired temperature at the bottom, and the temperature within the inner cover should be uniform throughout.

The hot track" construction of the invention in combination with the nozzle Construction provides a means for approaching such ideal heat distribution. In an annealer system employing such combination, the crculating atmosphere beats rapidly at the bottom of the inner cover and more slowly as it rises. The tendency for the circulating atmosphere to be hotter at the top of the inner cover is very materially reduced but not entirely eliminated in the system. However, with the intense concentration of heat made possible by the hot track, the inner cover can be made considerably hotter at the bottom than at the top by the increased radiation from the inner cover area looking at the hot track and thereby ofiset the convection eect.

The intense radiation heat is localized to the bottom portion of the inner cover due to the shielding effect of the upper wall of the recess which essentially constitutes an inverted step or shelf. .Such radiation shielding not only reduces radiation to the upper inner cover portion but also increases the surface temperature of the walls of the recess to further increase the heat transfer by radiation to the lower inner cover portion. While some radiation heat Will be emitted from the bottom wall of the recess, the heat of any appreciable intensity will be transferred within the area bounded by the ray 39 indicated in FIG. l.

The high heat release at the chamber bottom decreases heat available for release by the ascending combustion gases thus eecting a diminishing gradation of heat release to progressively higher portions of the inner cover. The diminution of heat release is due to the simple fact that there is less heat available because the inner cover wall absorbs the maximum amount where the maximum 7 amount is available. Better utilization of fuel is thus effected since most of the available heat in the combustion gases has been released by the time they are exhausted.

While it is preferable for optimum results that the "hot track be used in combination with the nozzle construction, it is to be understood that either may be employed without the other and yet result in improved annealer performance.

The nozzle Construction of the invention comprises a peripherally continuous flange 6& spaced inwardly from and cooperating with the side wall 13 of the inner cover 11 to define a nozzle 61 for directng the circulating gases in paths contiguous to said side wall 13. While in some instances a horizontal flange which seats on the top plate 19 to form a closed passage -from the base to the inner cover will sufce to direct the gases contiguous to the side wall, it is preferable to utilize a vertical portion in connection therewith to more definitely define the path of the gases. To insure that the horizontal portion 62 of the fiange 6@ will seat properly upon the top plate 19 as the inner cover is moved from one base to another, the vertical leg 59 of fiange 6& is provided with slotted holes 63 so as to be vertically adjustable and to compensate for any variation in height between the plates 19 and 26 from one stand to the next. As the hood 11 is removed from the base 15, the weight of the flange 60- will cause the top of the slotted hole 63 to seat on the fastening means, thereby dropping the flange 66 to its lowermost position. When the hood is moved to and disposed over another base, the flange will seat first upon the plate 19 and the hood will continue to move downward until it seats upon the base 15.

The vertical portion of fiange 60 is preferably of a height which substantially corresponds to the elevation at which the high radiation heat release heretofore described, occurs. Such Construction deters burning of the work charge opposite the area of intense heat release. The vertical portion also constitutes a re-radiation means to effectively transfer heat to the circulating gases passing through the nozzle.

In the annealer as shown in FIG. 3, the inner cover 11 is shown having a fixed annular fiange 70 comprsing the nozzle which also acts as a means of supporting the inner cover 11 on the base .15. In this embodiment, the lowermost portion of the inner cover is formed with a peripheral fiange which extends beyond the base and protrudes into a trough 71. The trough contains a liquid sealing means 72 so that the combustion chamber is sealed by virtue of the flange being immersed in said liquid 72. The burners 34 and hot track 35 are shown as being incorporated in the inner cover 11 rather than in the peripheral wall 16 as in the previous embodiment.

It is' readily understood that the flange cooperating with the inner cover to define a nozzle may comprise a part of the stationary base. However, in order to insure that the same as well as concentric spacingis maintained from base to base, it is preferable that the flange be made an integral part of the inner cover. Such Construction also results in the saving of expensive alloy material in that only one flange may serve several bases.

In' order to improve the circulation to the bottom edges of the bottom coil of a stack of coils, a series of vanes are provided defining gas passages to direct the gases from the perphery of the bottom coil to the center and hence to the fan. While an individual Separator employing vanes may be utilized for this same function, it is advantageous to incorporate such vanes in the base as an integral part thereof so as to reduce handling time.

The Construction of the nvention provides several desirable advantages. The hot track" serves not only as a combustion chamber wherein firing stability is maintained even when looking at a cold charge but also serves as a means of concentrating the heat released to the bottom 8 coil. the heating chamber results in better fuel utilization in that the fine gases are exhausted at reduced temperatures without losing the effective heat of combustion, Supplying a portion of the air through the radial port serves as a means of regulating the distribution of temperature from top 'to bottom of the combustion chamber without effecting the ring rate. The nozzle provides a means for matching the heat transfer inside the inner cover opposite the "hot track and also serves as a means 'for eectively wiping' the heat from the inner cover surface without efiecting the radiation heat transfer. The improved efficiency of the invention is manifested in the reduced time for completing the anncaling cycle in an annealer employing the invention.

We claim:

l. In a recirculating atmosphere furnace having a base, an inner cover on said base and forming therewith a heating chamber, a fan in the base for circulating atmosphere in the chamber, a retractory lined heating outer cover disposed over said inner cover and on said base, the combination which comprises: means for delivering an annular concentration of heat to a first zone in said chamber, second means for delivering a concentration of heat to a second zone in said chamber said second zone being above said first zone; first temperature responsive means responsive to temperature in said first zone; second temperature responsive means responsive to temperature in said second zone; proportioning means responsive to said first and second temperature responsive means for proportioning delivery of heat between said first and second zones; control means responsive to temperature in said chamber for controlling the total heat delivered to said chamber to maintain a substantially constant predetermined temperature therein; and means for directing the circulating atmosphere in the chamber contiguous to the side wall surface of the inner cover locatedin said first zone.

2. Apparatus for supplying heat to the inner cover of a recirculating atmosphere furnace having a base for supporting a work charge, a portable inner cover on said base and forming therewith a heating chamber, and a fan in said base for circulating the atmosphere in said chamber, in combination: means for delivering an annular concentration of heat to a first horizontal zone located near the bottom of said chamber and to a second horizontal zone in said chamber, said second zone being above said first zone; means responsive to temperature in said chamber 'for controlling the delivering means to maintain said chamber at substantially a predetermined temperature; and means for proportioning the delivery of heat between said first and second zone independently of the rate of supply thereor" as determined by said control means.

3. Apparatus for supplying heat to the inner cover of a recirculating atmosphere furnace having a base for supporting a work charge, a portable inner cover on said base and forming therewith a heating chamber, and a fan in said. base for circulating the atmosphere in said chamber; in combination: first means for delivering an annular concentration of heat to a first horizontal zone located near the bottom of said chamber; second means for deliverin'g a concentration of heat to a second zone in said chamber. said second zone being above said first zone; first temperature responsive means responsive to temperature in said first zone; second temperature responsive means responsive to temperature in said second zone; proportioring means responsive to said first and second temperature responsive means for proportoning delivery of heat between said first and second zones; and control means responsive to the temperature in said chamber for controlling the total heat delivered to said chamber to maintain a substantially constant predetermined temperature therein.

4. In a recirculating atmosphere furnace having a base, an inner cover on said base and formin; therewth a Such concentration of heat release to the bottom of i U heating chamber, a fan in the base for circulating atmosphere in said chamber, a refractory lined heating outer cover dsposed over said inner cover and on said base and adapted to supply heat to said inner cover for heating work theren, the combination which comprises: a cen-.

trally apcrtured bottom plate on said base for supporting said inner cover; a centrally apertured top plate on said base for supporting the work to be heated; vanes interposed between said plates defining passages from the center of said base to the periphery thereof, a peripherally continuous flange spaced inwardly from and cooperating with the side wall of said inner cover to define a nozzle for directing the atmosphere in paths contiguous to said side wall, and wherein said fiange has vertical and horizontal portions, and is mounted to said inner cover in a manner as to be self-adjusting in a vertical direction and to seat the horizontal portion on said annular top plate and thereby form a closed passage from the base to the inner cover; and a deflector structure incorporated in the base for initially directing the atmosphere longitudinally of said inner cover.

S. A combination according to claim 4, comprising heating means having an inverted step or shelf on the heating outer cover whereby radiant heat is released directly to the outside surface area of the inner cover which is adjacent to the vertical portion of the nozzle flange.

6. Apparatus for supplying heat to the inner cover of a recirculating atmosphere furnace having a base for supporting a Work charge, an inner cover on said base and forming therewith a heating chamber, said inner cover comprising corrugated side wall members having regularly spaced longitudinal convolutions of increased depth, a top wall, a peripherally continuous flarge having vertical and horizontal portions, means securing the vertical portion of said fiange to the side wall convolutions of increased depth to define passages between said flange and said side wall and a f an in the base for circulatng the atmosphere in said chamber comprising, in combination: a refractory lined heating cover for disposition over said inner cover and on said base, and having a peripheral recess in its refractory portion; and burner means firing a mixture of fuel and air into said peripheral recess in a manncr to isolate the burning mixture from the surrounding flue gases and cause said burning mixture to initially wipe the walls defining said recess, said recess walls being adapted to emit radiant heat directly to said inner cover.

7. Apparatus according to claim 6 wherein the securing means of the side walls eXtend through slots in the vertical portion of the flange to permit floating vertical adjustment of said flange.

8. In an annealing furnace having an inner cover, a base and a refractory lined outer cover, wheren said outer cover comprises a portable hood portion and a stationary upstanding peripheral wall portion extending from the base, means for controlling vertical heat distribution between said covers while maintaning constant heat input comprising: an annular, substantially horizontal, channel located in the hood refractory next adjacent said base; a single horizontal row of burners tangential to said channel and arranged to fire thereinto; radial ports in the refractory for ernitting air to the space between said inner cover and said outer cover; a fuel supply source for said burners; an air supply source; proportioning means for maintaining a constant portion of air and fuel flowing from said sources; and control means for proportioning the air between said burners and said ports.

9. In an annealing furnace having an inner cover, a refractory lined outer cover, and a base, means for varying vertical heat distribution between said covers while maintainng constant heat input comprising: an annular, substantially horizontal, channel located in the refractory; burners tangential to said channel for firing thereinto; radial ports in the refractory providing passages into the space between said inner cover and outer cover; a single air supply source for said burners; a single fuel supply source for said burners; proportioning means for mantaining a proportion for substantially complete reaction by combustion of air and fuel flowing from said sources; means for diverting a portion of the flow from one of said two sources and for delivering such diverted portion to said ports; and control means for varying the rate of flow to said ports relative to the rate of flow to said burners.

10. In an annealing furnace having an inner cover, a refractory lined outer cover, and a base, means for varying vertical heat distribution between said covers while mantaning constant heat input comprising: an annular, substantially horizontal, channel located in the refractory; burners tangential to said channel for firing thereinto; radial ports in the refractory for emitting air to the space between said inner cover and outer cover; a single air supply source for said burners; a single fuel supply source for said burners; proportioning means for mantaining a proportion for substantially 'complete reaction by combustion of air and fuel owing from said sources; means for diverting a portion of the flow from said air source and for delivering such diverted portion to 'said ports; and control means for varying the rate of flow of air to said ports relative to the rate of flow of fuel and air to said burners.

References Cited in the file of this patent UNITED STATES PATENTS l,473,491 Manning Nov. 6, 1923 1,671,352 De Guise May 29, 1928 2,184,975 MacConville et al. Dec. 26, 1939 2,220,797 Bates et al. Nov. 5, 1940 2,224,544 Keller Dec. 10, 1940 2,293,550 Kells Aug. 18, 1942 2,485,995 Armstrong Oct. 25, 1949 2,491,704 Bloorn Dec. 20, 1949 2,499,846 Carter Mar. 7, 1950 2,529,609 Jacob Nov. 14, 1950 2,556,081 Hartman June 5, 1951 2,600,094 Lone June 10, 1952 

